Integrated circuits (also referred to as dies or chips) are typically tested on wafer level subsequent to manufacturing (so-called “wafer probing” or, short, “probing”). During the testing, a final application environment may be simulated electrically. To this end, dies on a wafer may be mechanically and electrically contacted with one or more probes (e.g., a probe card including a plurality of probes) to send in and read out electrical signals via the probes. The probes may be configured as needles, e.g., cantilever needles, which may contact one or more contact pads (also referred to as bonding pads or, short, pads) of the dies.
Recent chip manufacturing technologies tend to place the contact pads over active areas of the chips in order to save chip area (sometimes referred to as PoAA (Pad Over Active Area) configuration or design). Probes (e.g., needles) contacting the pads during wafer probing exert mechanical forces (contact forces) on the pads, which may cause damage to the pads and/or layers below the pads. For example, cracks may occur in an insulating layer (e.g., oxide layer) below a pad, which in turn may cause short circuits between the pad and an electrically conductive line below the pad.
Conventional methods for detecting damages caused by probing require, for example, a) measurement of pad penetration depths (scrub depths) by means of confocal microscopy, or b) chemical preparation of tested dies and subsequent optical inspection/control with respect to damages in the insulating layer (e.g., oxide) below the pads. Both methods may need to be carried out manually (which may require considerable effort, may be expensive and unreliable), and the results may often be open to interpretation. Investigations by means of chemical preparation may commonly require several days up to weeks, or may not be possible for some products.
Due to the relatively high effort involved in the aforementioned conventional methods, process windows may oftentimes only be determined with a relatively low number of parameter variations. This may result in an over dimensioning (e.g., with respect to pad geometry, pad material, expensive needle technology) in order to guarantee the necessary reliability. Furthermore, an optimum solution may not be found systematically.